This invention is in the mechanical field and relates to tank cars used to transport oil on railroads or highways.
Railroads and highways are widely used in many nations to haul crude oil and oil products to and from pileline terminals, and to locations that are not served by major pipeline systems. This invention is limited to the over-land hauling of oil, in bulk (i.e., oil loaded directly into a cargo tank of a tank car for hauling; this excludes oil subdivided into other containers such as barrels or cans, and oil used by a transport device for lubrication or fuel). As used herein, all terms such as hauling, transport, tanks, tank cars, or cargo, are limited to transportation across land, on railroads or on highways or other surface roads. Such terms do not involve or include water-borne shipping, and they do not involve or include pumping of oil through pipelines.
Hauling of crude oil or refined products across railways or highways requires special types of rolling tank containers, referred to herein as a "tank car" regardless of whether it is adapted for railway or highway use (in some countries, tank cars are referred to as cisterns). A typical tank car for use on a railway comprises a cylindrical steel container with one or more inlet/outlet ports on the top and a drainage port on the bottom, mounted on a chassis that comprises steel railroad wheels and conventional railway couplings at both ends, so that the tank car can be added or inserted into a line of train cars. Railway tank cars may have certain types of fixed piping systems, but they usually do not carry pumps or flexible hoses, since their cargoes are loaded and unloaded only at railroad terminals, which provide the necessary pumping equipment.
Typical railway tank cars used in America are slightly less than 15 feet tall (to allow travel beneath overpasses) and 11 feet wide, and usually have a cargo capacity ranging from about 12 to about 22 thousand gallons, depending on the length of a specific tank car. Accordingly, railway tank cars are not meant to serve small facilities; instead, they're used to transport oil only to large industrial facilities with rail terminals, such as oil refineries or pumping stations, electric power generating plants, or very large factories.
Extensive additional information on the design of railway tank cars is provided in Section C of the Manual of Standards and Recommended Practices, issued by the Assn. of American Railroads (AAR, Washington, DC). Another illustrated reference work, available in many libraries, is the Car and Locomotive Cyclopedia (compiled by AAR and published by Simmons-Boardman, New York, 1974).
A tank car for use on a highway or other surface road (sometimes called a tank trailer) provides a similar cylindrical tank (which are usually smaller than on railroad tank cars), a chassis, rear wheels with rubber tires, and an attachment device in the front that allows the trailer unit to be coupled to a conventional diesel highway tractor unit. Unlike railway tank cars, a highway-type tank car is usually provided with one or more flexible loading hoses and a pump, which can be driven either by a gasoline or diesel motor carried on the trailer, or by a mechanical connection that allows the main engine of the tractor unit to drive the pump. By carrying their own pumps and hoses for loading or unloading cargo, highway tank cars can serve small facilities that do not have pumping and handling devices.
Some tanks used in tank cars are not completely cylindrical. Highway tank cars in particular often have elliptical cross-sections for better weight distribution, since a lower center of gravity reduces the risk of rollover in an accident. Some tanks also have slanted bottom surfaces to promote drainage, or sump depressions on the bottom for collecting sediments.